The Role of Gαq-Mediated Stress Granules in Neuron Function

Jackson, Lela

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The Role of Gαq-Mediated Stress Granules in Neuron Function

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Phospholipase Cβ1 (PLCβ1) is a multifunctional protein that both localizes to the plasma membrane and binds to cytosolic proteins. PLCβ1’s traditional role takes place on the plasma membrane after being activated by G proteins in response to hormones and neurotransmitters, leading to an increase in intracellular calcium. Surprisingly, we discovered a population of PLCβ1 that binds to cytosolic proteins, and ~1/3 of these binding partners are stress granule (SG) proteins. SGs are dynamic membraneless organelles that shift untranslated mRNA and proteins into cytosolic aggregates when mammalian cells experience environmental stress. This is an advantageous process done to temporarily conserve energy until stress is relieved, but premature or irreversible SG formation has potential to become detrimental to gene regulation and therefore induce onset of disease. In the cytosol, PLCβ1 binds to SG proteins such as eukaryotic translation initiation factor 5a (eIF5a), polyadenylate binding protein 1 (PABPC1) and Ras GTPase activating binding protein 1 (G3BP1) in addition to a member of the RNA induced silencing complex (RISC) component 3 promoter of RISC (C3PO), as well as the multifunctional protein Argonaut 2 (Ago2). We found that PLCβ1 regulates the formation of SGs as it shuttles from the cytosol to the plasma membrane during G protein activation. The release of these binding partners due to loss of cytosolic PLCβ1 leads to the initiation of SG complexes and the promotion of RNA-induced silencing. It is also known that C3PO-PLCβ1 complexes are necessary to maintain a differentiated phenotype in neuronal cells. However, the interactions between PLCβ1, C3PO and Ago2, the role this ternary protein complex play in RNAi, and its contribution to neuronal differentiation had not been well studied. Additionally, the nature of SG formed by PLCβ1, and in turn consequence of Gαq stimulation were unknown. This thesis seeks to understand how re-localization of cytosolic PLCβ1 in response to Gαq stimulation by neurotransmitters and environmental stress influences neuronal stress response, RNA transcription and gene silencing, and may influence changes in cytosolic protein interactions, specifically involving PLCβ1, Ago2 and C3PO.

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